Today I learned@Cybertec

Lorenz Henk

Full Stack Developer

Typescript ReturnType

Typescript includes several useful utility types to enhance the type declarations of your code-base.

The ReturnType function is one of my favorite ones, as it helps reduce type definition duplication.

Suppose you have the following function definition:

type IsInText = (
  text: string
) => (
  term: string,
  minCount: number,
  maxCount?: number,
  caseSensitive?: boolean
) => boolean

Now we want to write a function allTermsInText, that takes the function returned by isInText as an argument. It should be used like:

allTermsInText(["Typescript", "awesome"], isInText("Typescript is awesome!"))

Here is the definition without the utility type:

type AllTermsInText = (
  terms: string[],
  search: (
    term: string,
    minCount: number,
    maxCount?: number,
    caseSensitive?: boolean
  ) => boolean
) => boolean

And here the same function definition, but using ReturnType for the parameters:

let AllTermsInText = (terms: string[], search: ReturnType<IsInText>) => {
  return !terms.find(term => !search(term, 1))
}

Pretty Printing JSON

JSON is everywhere, but reading nested JSON without proper formatting can be a nightmare.

PostgreSQL

The function jsonb_pretty allows you to pretty print jsonb data.

\pset format unaligned
SELECT jsonb_pretty('{"name": "Lorenz", "team": {"name": "Team #1", "color", "blue"}}'::jsonb);

{
    "name": "Lorenz",
    "team": {
        "name": "Team #1",
        "color": "blue"
    }
}

Javascript

If you work with JSON data in Javascript, you surely know the function JSON.stringify. But did you know it can prettify your JSON as well?

JSON.stringify({"name": "Lorenz", "games_won": 4, "games_lost": 1}, null, 4)
                                      // number of spaces for indentation ^

{
    "name": "Lorenz",
    "games_won": 4,
    "games_lost": 1
}

Python

Python's json module adds functions to work with JSON.

>>> import json
>>> print(json.dumps({"players": [{"name": "Lorenz"}, {"name": "Philip"}]}, indent=4))

{
    "players": [
        {
            "name": "Lorenz"
        },
        {
            "name": "Philip"
        }
    ]
}

Command line using Python

You can also directly run the tool exposed by the json module from the command line:

$ echo '{"name": "Lorenz", "has_eyes": true}' | python3 -m json.tool

{
    "name": "Lorenz",
    "has_eyes": true
}

Delete already merged branches

The code example below shows how to delete all branches which have already been merged into the current branch:

$ git branch
  feature-1
  feature-2
  feature-3
* master

$ git branch --merged
  feature-1
* master

$ git branch --merged | egrep -v "(^\*|master)"
  feature-1

$ git branch --merged | egrep -v "(^\*|master)" | xargs git branch -d
Deleted branch feature-1 (was 1d7fd54).

Check out this great Stack Overflow answer for more information.

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